In the past, longitudinally pumped dye laser arrangements have been used, such lasers being different from transversely pumped dye lasers. One advantage of the longitudinally pumped dye laser arrangement compared to transversely pumped dye lasers is that an extremely small depth of dye solution may be used to produce short output pulses. All of these earlier longitudinally pumped units are either quite expensive or have a large number of optical components, which require critical alignment. In "Topics in Applied Physics", Volume 1, Dye Laser by F. P. Schafer (2nd edition), 1977, several longitudinally pumped dye laser arrangements are illustrated at page 39. In all of these arrangements, the output radiation emerging from the dye laser cell travels in the same direction and is essentially collinear with the input pumping beam. In order to create a resonator cavity and to suppress the input pumping beam in the output beam, it is necessary to coat the surfaces of the cavity with expensive dielectric, multi-layer mirrors which selectively pass a desired radiation wavelength. The surface admitting the input pumping beam must be relatively transparent to light at the input pumping beam wavelength and the surface at the opposite and emerging end of the cavity should have a dielectric coating with a high reflectivity for the pumping beam wavelength. Conversely, at the lasing radiation wavelengths, the input surface admitting the pumping beam must have a high reflectivity and the surface from which the lasing radiation emerges must have a lower reflectivity so as to allow a portion of the dye lasing radiation to pass out of the optical resonator cavity.
A different longitudinally pumped dye laser arrangement is disclosed by H. Salzmann and H. Strohwald, Physics Letter, 57A (1976), 41. They show an arrangement consisting of a lasing medium dye solution contained between a mirror surface and a prism. The incoming pumping beam is reflected by a first mirror onto the prism's surface and refracted down into the dye solution where lasing activity takes place. The resulting lasing radiation travels through the prism, emerges from the prism at a different location than the pumping beam entered, is refracted out into free space and reflected by a second mirror into its desired direction. This placing of a prism in the optical path of a dye laser cavity has been used previously, as disclosed in the Yarborough et al, U.S. Pat. No. 3,873,941 at column 2, lines 24 through 36. Furthermore, the Salzmann et al arrangement requires that the first and second mirrors must be adjusted independently of one another for proper optical alignment.
G. Veith and A. J. Schmidt in Optics Communication, Volume 30, No. 3, September, 1979, disclose a transversely pumped dye laser arrangement where its output is amplified by a longitudinally pumped amplifier cell. The medium in the amplifier cell is excited to a level below the threshhold which is required for lasing action to occur. The dye laser pulse to be amplified enters the amplifier cell and causes stimulated emission to occur in the amplifier cell. This action results in the amplification of the dye laser pulse.
In the amplifier portion of their set up, a single lens was used to focus the exciting beam into the amplifier cell and to collect the amplified pulse emerging from the cell. A second lens was used to focus the dye laser pulse to be amplified into the opposite side of the amplifier cell than the beam to excite the dye solution enters from. Since the dye laser pulse to be amplified enters the amplifier cell from the opposite side of the cell than the amplified pulse emerges from, it is apparent that no mirror may be used to reflect the amplified pulse towards the first lens. Special care had to be taken to obtain a good spatial overlap between the focal region of the dye laser pulse to be amplified and the gain region. This is due to the fact that the dye laser pulse is entering the amplifier cell from the opposite side of the cell than the beam to excite the dye solution enters from. Also, since it is necessary for the length of the amplifier cell to be of sufficient magnitude so that a suitable amplification factor can be obtained, the alignment problems are further aggrevated.
Although the prior art systems do function adequately, they are expensive, complicated, difficult to align and consist of many parts. The present invention seeks to mitigate these shortcomings.